Mann-Rea will face the wrath of the judiciary after punching Stormers prop Oli Kebble with 17 minutes left in the game and when the Brumbies were trailing by just five points.

It was a huge turning point in a heated clash at Newlands, with controversial referee decisions capping off the Brumbies' first loss of the Super Rugby season.

The Brumbies are expected to ask SANZAAR referees' boss Lyndon Bray for an explanation on multiple Jaco Peyper howlers, which contributed to the 20-point defeat.

But Mann-Rea was the first to put his hand up and say sorry to the rest of the team after the match.

The Brumbies have put rake Robbie Abel on standby to fly to South Africa if Mann-Rea is suspended while Ita Vaea is already in the Republic after being called up to replace Jarrad Butler, who is out for the next six weeks with a knee injury.

It is hoped Henry Speight (face) and Tomas Cubelli (dislocated finger and knee) will be fit to play the Free State Cheetahs on the weekend as the Brumbies aim to get their winning momentum back.

Mann-Rea's punch led to him being sent off before Peyper made some baffling calls, including awarding a match-winning try to Dillyn Leyds despite the Stormers winger appearing to drop the ball before grounding it across the line.

Peyper told Brumbies players on the field: "He's carrying it, so he doesn't have to have control. When you carry it, you just have to be in contact with it." Then he added: "It's not about control when you carry it ... There's no clear separation between arm and ball, therefore it's a try."

Rugby law 22.1 (a) states that it is a try if "a player grounds the ball by holding the ball and touching the ground with it, in in-goal. 'Holding' means holding in the hand or hands, or in the arm or arms. No downward pressure is required."

Brumbies coach Stephen Larkham said: "I need an explanation on the laws of [controlling the ball when scoring a try]. There were other [decisions] that were spot on and that's what you get.

"A number of decisions - the Stormers taking the ball into touch but then getting the lineout throw, the red card, the try, a couple of ones at the breakdown - it was one of those games where it just didn't eventuate for us.

"We had no momentum through the game through some of our own fault and through some of those decisions. Some of them were a little bit perplexing."

Mann-Rea will find out his potential punishment on Sunday night (AEDT) before the club decides whether or not to fight the suspension. One of the key points will be whether the SANZAAR judiciary officer deems Mann-Rea used his forearm or just punched Kebble.

Tensions were simmering between the Brumbies and Stormers, and Mann-Rea reacted after being pushed by lock Eben Etzebeth with Kebble coming over the top to join in.

It came when the Brumbies were behind just 16-11. The Stormers then booted clear and scored 15 unanswered points to finish the game.

"Bongo [Mann-Rea's] punching was straight-up silly. It doesn't matter what sparked the incident, he shouldn't have thrown a punch. He's very disappointed, it was a usual sort of altercation as you come out of a maul with a bit of push and shove," Larkham said.

"[Mann-Rea] has apologised ... he felt like he let everyone down and he's bitterly disappointed he threw a punch. But for mine, I'll have to look at it again, I don't think it should have been a red card."

The Brumbies were left battered and bruised after a brutal encounter against the Stormers, but the 20-point margin did not reflect the closeness of the game.

The result was in the balance at 19-11 with four minutes left when Leyds flew across the line but was tackled by Brumbies winger Joseph Tomane before he could get the ball down.

The final nail in the coffin came when Stormers replacement prop Vincent Koch scored after the siren to complete the win.

"We came up against a spirited Stormers side, we'll go back to the drawing board," said Brumbies front-rower Scott Sio.

"We couldn't match them at the breakdown and we have to work on that this week. We were ready. At the end of the day the Stormers took it to us and we didn't front up. That's what can happen against a strong side like the Stormers."

Butler will return to Canberra after injuring his knee at training last week, allowing Vaea to rejoin the squad after recovering from surgery on his dislocated finger.

The Brumbies fought their way into the contest after being strangled out of the first half, and scored when Tevita Kuridrani walked through a massive hole then threw a perfect 20-metre pass to Henry Speight to go across the line untouched.

But the good news didn't last long as Kurt Coleman booted penalties and then the Stormers took advantage in the dying minutes to inflict more pain on the Brumbies.

"We were in there right until the end, but it was just a little bit of detail and being able to execute [that was missing]," Lealiifano said.

"I thought we handled their kicking game, tactically I think both teams were right in it and it was a genuine contest. Credit to the Stormers, they played really well."

AT A GLANCE

CAPE TOWN STORMERS 31 (Siya Kolisi, Dillyn Leyds, Vincent Koch tries; Kurt Coleman 3 penalties; Kurt Coleman; Jean-Luc du Plessis conversions) bt ACT BRUMBIES 11 (Tevita Kuridrani try; Christian Lealiifano 2 penalties) at Newlands, Cape Town on Sunday morning (AEDT). Referee: Jaco Peyper.